In order to measure the running condition of an automobile, state of movement of a robot, or the like, use is made of an angular velocity sensor provided with a vibration type sensor element.
FIGS. 10A and 10B are views showing a conventional sensor element, in which FIG. 10A is a plan view, and FIG. 10B is a cross-sectional view taken along the line VI-VI in FIG. 10A.
The sensor element shown in the above figures has a weight part 101, a frame-shape fastening part 102 surrounding the weight part 101, beam parts 103 connecting the weight part 101 to the fastening part 102, and piezoresistive elements 104 formed on the beam parts 103.
The weight part 101, fastening part 102, and beam parts 103 are integrally formed by machining a silicon substrate.
Further, the piezoresistive elements 104 are formed by implanting boron into the surface of the silicon substrate.
In such a sensor element, if an angular velocity around an axis of rotation parallel to the longitudinal direction of beam parts 103 is generated in a state where the beam parts 103 are made to vibrate, the weight part 101 moves. Along with that, the beam parts 103 deform, therefore the piezoresistive elements 104 deform.
The angular velocity is detected based on a change of the resistance value due to the deformation of these piezoresistive elements 104.
Accordingly, in order to improve the detection sensitivity of the angular velocity, the beam parts 103 may be made easier to deform. The trick in the past has been to make the volume of the weight part 101 larger (see for example Japanese Patent Publication No. 2003-172745).
This type of sensor element can detect the angular velocities in the three X-, Y-, and Z-axial directions by the piezoresistive elements 104 arranged on the beam parts 103 and the interconnects connected to those.
Further improvement of the detection sensitivity is being demanded from sensor elements. In order to improve the detection sensitivity, reduction of the variation of sensitivity in the three axial directions is effective.
The present invention was conceived of under the above circumstances and has as an object thereof to provide a sensor with small variation of sensitivity in the three axial directions.